1. Field of the Invention
The present invention relates to a printed-circuit board that includes a capacitive element embedded in a substrate resin layer inside a substrate that includes a plurality of wiring layers laminated with the substrate resin layer interposed in between, and to a manufacturing method of such printed-circuit boards.
2. Description of the Related Art
Printed-wiring boards and flexible substrates are examples of the substrate (hereinafter, “printed-circuit board”) that is incorporated in an electronic device with an electronic circuit that includes the wiring formed by using a technique such as printing. Generally, such printed-circuit boards are formed by mounting simple passive element components such as capacitors and inductors during the formation of the substrate. Because the capacitance and inductance of some of the simple component capacitors and inductors are larger than those of the passive elements formed in a semiconductor integrated circuit (IC), it is not easy to replace the simple passive element components with the capacitive elements in the semiconductor integrated circuit.
For this reason, large numbers of simple passive element components are typically mounted on a printed-circuit board, in addition to a semiconductor integrated circuit. However, the mount area of the printed board needs to be increased as the number of components that cannot be integrated into the semiconductor integrated circuit (IC) is increased. Many of such simple passive components that cannot be provided as an IC have heights that exceed the mount height (the dimension vertical to the mount face) of the semiconductor integrated circuit.
For these reasons, various passive elements mounted on a printed circuit are considered as a large obstacle that prevents miniaturization of electronic devices.
Capacitor, a representative passive element, must satisfy the requirements of both miniaturization and high-frequency. This has led to the development of a technique by which a separately produced simple component is embedded in a substrate. There has also been active research directed to realizing a capacitor integrated in a substrate.
A known example of such a capacitor integrated in a substrate is a thin capacitor of an MIM (Metal-Insulator-Metal) structure in which a lower electrode is formed using the wiring layer of the multilayer wiring structure inside a printed-circuit board, and in which a high-relative permittivity dielectric film and an upper electrode are laminated on the lower electrode (see, for example, JP-A-2008-78547 (Patent Document 1)).
Generally, the base material of the printed-circuit board, specifically, the base material of the substrate composite including a substrate interlayer resin layer made of an organic compound polymer (hereinafter, “substrate resin layer”) does not withstand high temperatures. It is therefore important to form the metal electrode films and the dielectric film by low-temperature deposition such as low-temperature sputtering. Further, because the dielectric film deposited by low-temperature deposition generally does not turn into crystals immediately after the deposition (as-deposited state), the film has low relative permittivity (for example, 5 or less). This necessitates a heat treatment for the dielectric film after the deposition to improve relative permittivity. High temperatures of 400° C. and higher are generally used for the heat treatment. It is therefore very difficult, if possible, to use the low heat-resistant polymer as the base material of the substrate composite (printed-circuit board).
As a solution to this problem, amorphous materials, such as BiZnNb amorphous metal oxides, that have high relative permittivity even in low-temperature deposition have been proposed (see, for example, JP-A-2007-13090 (Patent Document 2)).
Facing targets sputtering as a low-temperature and high-speed deposition method is also proposed (see, for example, Japanese Patent No. 2716138 (Patent Document 3)).